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Old 09-10-2019, 12:30 AM
ric62 is offline
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Geometry and concrete blocks


I am thinking of getting concrete retaining wall blocks that are angled on both ends, I was wondering if I laid them side to side how big would the circle be. Any ideas on a formula so I don't have to do to the store and lay them out?
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Old 09-10-2019, 12:42 AM
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I’m not an expert but I’m pretty sure the angle is to allow several different radii. In other words, I don’t think it’s necessary to place the angled ends flush.
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Old 09-10-2019, 12:42 AM
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You haven't said how the angles are specified, but let's say that it's a number of degrees off perpendicular. For example, say that each side is 3 degrees short of the 90 degrees you'd get for a straight-cut block.

Take 180 and divide by this angle to get the number of blocks around. For 3 degrees, that's 60 blocks.

Divide by 3.14 to get the number of blocks across. That comes to 19 in this example.

Then, multiply by the length of the block. If they're 1 foot long, then the circle is 19 feet in diameter.
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Old 09-10-2019, 06:58 AM
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Originally Posted by ric62 View Post
I was wondering if I laid them side to side how big would the circle be. Any ideas on a formula so I don't have to do to the store and lay them out?
I think the blocks are not designed to be laid side to side. You fill the gap up with pebble stones or the like to get good drainage. If you stick them side to side, my guess is you will get something like a 6-8 ft circle but I wouldn’t advise doing that.
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Old 09-10-2019, 07:35 AM
Joey P is offline
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Quote:
Originally Posted by ric62 View Post
I am thinking of getting concrete retaining wall blocks that are angled on both ends, I was wondering if I laid them side to side how big would the circle be. Any ideas on a formula so I don't have to do to the store and lay them out?
Find out what brand they have and check out their website or check the website of the store you're going to. It's going to be different from brand to brand (I assume), but I've seen plenty of displays (online and IRL) that show you exactly how big of a circle the angled blocks will make if you butt them up against each other.
But even ignoring that, you can cut them to change the angle to whatever you want it to be. A good masonry angle grinder blade can be had for about $10 and will cut a block in 30 seconds or so.
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Old 09-10-2019, 07:37 AM
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If you stick them side to side, my guess is you will get something like a 6-8 ft circle but I wouldn’t advise doing that.
Maybe the OP is making a fire pit or is just trying to figure out how big of a corner they're going to end up with on a retaining wall if they don't cut any of them.
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Old 09-10-2019, 08:00 AM
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Maybe the OP is making a fire pit or is just trying to figure out how big of a corner they're going to end up with on a retaining wall if they don't cut any of them.
You are right. If that’s the case, then go to the manufacturer’s website and they will have a Chart like this one : https://www.allanblock.com/retaining...ius-chart.aspx

(The curve radius is dependent on the wall height since subsequent layers “lock” on to the lower layer)
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Old 09-10-2019, 11:31 AM
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(The curve radius is dependent on the wall height since subsequent layers “lock” on to the lower layer)
Not that it really applies here, but a chisel and hammer will knock that 'lock' off pretty quickly. I just put up some like this. In this picture, some of the bricks are upside down and you can see a lip opposite the curved side. That's what sets each course a little behind the one below it. When I go around bend, I'll chip that off, otherwise the brick is set too far back.
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Old 09-10-2019, 11:55 PM
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I am trying to make a circle. I think I can figure out the radius or diameter, if not I'll ask the people at the outdoor department.
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Old 09-11-2019, 10:45 AM
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The angle that each end is off 90 degrees creates, essentially, a piece of a triangle with the sides pointing to the center of the circle. you need to know the angle. take two straight edges or boards, push them flat against the angled ends, and see where the two boards meet. That's the center of the circle, no math required (unless the radius is more than about 8 feet, too long for a plank - unlikely. )
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